Project Overview

Full Title
Stratification and Water Quality in the New Hope Arm of Jordan Lake, Chatham County, NC

Location
  Chatham County

Cooperating Agencies
Town of Cary, NC

Project Chief
Mary Giorgino
giorgino@usgs.gov

Period of Project
2012 - 2019

Team Members
Jessica Cain
Ryan Rasmussen

Science Topic
Increased Population and Water Resources

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Stratification and Water Quality of Jordan Lake

Summary

Winter at Jordan Lake. Photo courtesy of Doug Harned, USGS.

The New Hope arm of Jordan Lake, located in Chatham County, North Carolina, serves as a drinking-water supply for the Towns of Cary, Apex, and Morrisville. The reservoir is listed as impaired due to nutrient over-enrichment and occasionally experiences algal blooms and fish kills.

Water quality in Jordan Lake varies with depth, particularly during warm months when the lake stratifies.

• Water near the surface typically is well oxygenated and supports abundant algae.
• Bottom waters are oxygen-poor and contain elevated levels of dissolved iron, manganese, and nutrients.

Both scenarios can lead to high water-treatment costs and taste and odor issues.

The Town of Cary proposes to install an innovative, high-capacity, water-column mixing system in the New Hope arm of Jordan Lake during winter 2016-2017.

The vertical-mixing system is expected to enhance drinking-water treatment, alleviate algal blooms, and enhance recreational use by:

• Keeping the entire water column well oxygenated
• Lowering levels of dissolved iron and manganese
• Altering phytoplankton dynamics and the distribution of nutrients

However, if the system does not completely mix the water column as expected, nutrients transported upward from bottom waters could fuel algal blooms near the surface.

In order to evaluate effects of installing a vertical-mixing system on the New Hope arm of Jordan Lake, the U.S. Geological Survey (USGS) is documenting water-column stratification, chemical quality, taste and odor compounds, and phytoplankton characteristics before and after installation of a mixing system. This project is being conducted in cooperation with the Town of Cary, NC, and with support from the USGS Cooperative Water Program.

Objectives

The objectives of this study are to:

1. Evaluate the spatial and temporal scope of the vertical-mixing system's effects on lake stratification
2. Document concentrations of iron, manganese, nutrients, and taste and odor compounds before and after the installation of the mixing system